The purpose of the proposed research is to purify and characterize a tRNA sulfurtransferase system from a variety of rat tissues, including the liver and brain. This enzyme has been shown to be capable of transferring the sulfur from beta-mercaptopyruvate to tRNA in vitro. After the tRNA sulfurtransferase from normal adult rat liver has been examined, a comparison of the activities of this enzyme in adult, neonatal and fetal liver will be carried out. Later, similar comparative studies will be performed on a number of hepatomas and the corresponding host livers to determine whether there are any qualitative and/or quantitative differences in tRNA sulfurtransferase activities between normal and neoplastic tissues.